Ann Hallemans

Low vision affects dynamic stability of gait

The objective of this study was to demonstrate specific differences in gait patterns between those with and without a visual impairment. We performed a biomechanical analysis of the gait pattern of young adults (27 ± 13 years old) with a visual impairment (n=10) in an uncluttered environment and compared it to the gait pattern of age matched controls (n=20). Normally sighted adults were tested in a full vision and no vision condition. Differences are found in gait between both groups and both situations. Adults with a visual impairment walked with a shorter stride length (1.14 ± 0.21m), less trunk flexion (4.55 ± 5.14°) and an earlier plantar foot contact at heel strike (1.83 ± 3.49°) than sighted individuals (1.39 ± 0.08 m; 11.07 ± 4.01°; 5.10 ± 3.53°). When sighted individuals were blindfolded (no vision condition) they showed similar gait adaptations as well as a slower walking speed (0.84 ± 0.28 ms(-1)), a lower cadence (96.88 ± 13.71 steps min(-1)) and limited movements of the hip (38.24 ± 6.27°) and the ankle in the saggital plane (-5.60 ± 5.07°) compared to a full vision condition (1.27 ± 0.13 ms(-1); 110.55 ± 7.09 steps min(-1); 45.32 ± 4.57°; -16.51 ± .59°). Results showed that even in an uncluttered environment vision is important for locomotion control. The differences between those with and without a visual impairment, and between the full vision and no vision conditions, may reflect a more cautious walking strategy and adaptive changes employed to use the foot to probe the ground for haptic exploration.

Visual deprivation leads to gait adaptations that are age- and context-specific: II. Kinematic parameters

Significant differences exist between eyes open (EO) and eyes closed (EC) conditions in postural sway, self-selected dimensionless walking speed and duration of double support in both children and adults. The decrease in speed could be attributed to a decrease in dimensionless stride length. The question remains whether the slower gait is a reflection of fundamental changes in movement control in the absence of vision or it results from uncertainty or fear of falling. Studying the differences in foot and ankle kinematics between the two conditions may provide further information. In this study we compare the impact of visual deprivation on joint kinematics during locomotion in adults and children. Visual deprivation had a significant effect on the gait pattern of healthy children and adults. Differences included a more backward leaning position of the trunk, limited movement in the pelvis, reduced hip adduction during stance, increased flexion of the knee related to flat foot contact and reduced ankle plantar flexion at push-off. These differences indicate a more cautious walking strategy in the absence of vision, probably resulting from postural control problems. Although age also had a significant effect on gait in both EO and EC conditions, adults and children show little differences in their kinematic response to blindfolding.

Pressure Distribution Patterns under the Feet of New Walkers: The First Two Months of Independent Walking

In order to describe foot function during the first weeks of independent walking, spatio-temporal pressure distribution patterns were measured. These data give detailed information about roll-off of the foot, by determining the course of the center of pressure, and about load bearing, by calculating relative vertical impulses under the feet. During those first weeks of independent walking, roll-off is very unstable. Although infants can occasionally perform a mature roll-off, a consistent pattern has not yet developed and there is instability. To improve stability the entire plantar surface area contributes to load bearing – first, because a larger contact area will improve stability, and second, because a forward shifting of the load allows more muscular control to compensate for minor imbalances under the foot.

Mechanical energy in toddler gait - A trade-off between economy and stability?

SUMMARY Mechanical energy expenditure was investigated in children who are just learning to walk and compared with adult mechanical energy expenditure during walking. First, we determined whether the inverted pendulum (IP) mechanism of energy exchange was present in toddlers. It seems that new walkers partially make use of this energy saving mechanism, but it is less efficient than in adults. The reduced recovery values (R=40% at optimal speeds in toddlers compared to 70% in adults) can be explained by their low self-selected walking speed in combination with their tossing gait (large vertical oscillations of the body) and by the observation that during as much as 25–50% of the gait cycle kinetic and potential energy are oscillating in-phase. The second step was to calculate positive external mechanical work (Wext). Since the IP mechanism is less efficient in toddlers, more mass-specific positive work has to be performed to lift and accelerate the centre of mass than in adults walking at the same speed, even when differences in body size are taken into account. The amount of positive internal work (Wint,k) necessary to move the body segments relative to the centre of mass was the third parameter we calculated. In toddlers Wint,k is largely determined by the kinetic energy of the lower limb. Compared to adults, toddlers have to perform less mass-specific work per unit distance to accelerate the body segments since the upper body is kept relatively stiff during walking and there is no arm swing. Apart from work performed on the centre of mass and work performed to move the body segments relative to the centre of mass, when walking some work is also performed during double contact as both legs are pushing against each other. Two methods were used to calculate this amount of work, both leading to the same conclusions. Mass-specific work during double contact is small in toddlers compared to adults because of their low walking speed. Finally the total amount of mechanical work performed in toddlers was compared to the work production observed in adults. Wext seems to be the major determinant for total mechanical energy expenditure. At intermediate froude numbers work production is comparable between adults and toddlers, but at low and high froude numbers Wtot increases due to the steep increases in Wext. Despite the fact that mechanical work requirements in toddler gait are underestimated if work during double contact is not taken into account, it is not a major determinant of the energy cost of walking.

Development of independent locomotion in children with a severe visual impairment

Locomotion of children and adults with a visual impairment (ages 1-44, n = 28) was compared to that of age-related individuals with normal vision (n = 60). Participants walked barefoot at preferred speed while their gait was recorded by a Vicon(®) system. Walking speed, heading angle, step frequency, stride length, step width, stance phase duration and double support time were determined. Differences between groups, relationships with age and possible interaction effects were investigated. With increasing age overall improvements in gait parameters are observed. Differences between groups were a slower walking speed, a shorter stride length, a prolonged duration of stance and of double support in the individuals with a visual impairment. These may be considered either as adaptations to balance problems or as strategies to allow to foot to probe the ground.

Age-related changes in mechanical and metabolic energy during typical gait

The purpose of the study was to investigate and report age-related changes in walking energy expenditure using different methods of energy estimation. For 81 children and 16 adults (3-35 years) energy expenditure was investigated by using the following methods: analysis of energy changes of the centre of body mass (external and internal mechanical work), sum of segmental energies, sum of net joint work and gross and net metabolic cost, as well as net non-dimensional oxygen cost. Different methods of energy estimation not only show different outcome results but also different age-related changes. Significant changes were found for negative net joint work, external mechanical work and recovery as well as sum of segmental energies, until 9, 11 and 19 years respectively. Positive net joint work showed no differences between age groups and the differences for internal work did not suggest development. Metabolic energy showed significant changes until adult age. Gross cost decreases with increasing age in children and, although more gradually, still in adolescents. Net and net non-dimensional cost shows a more constant decrease with increasing age until adulthood. Therefore, the choice of estimation method and the use of age-related reference data when evaluating young patients should be carefully considered. For interpretation of oxygen consumption in children the use of net is superior to gross cost, but even after net non-dimensional normalization, age-related reference data should be used.

Growth of segment parameters and a morphological classification for children between 15 and 36 months

This study is part of a research program that aims at a better understanding of the influence of individual morphological differences and physical growth on development of independent walking in toddlers. As morphometric and segment inertial parameters for toddlers aged between 15 and 36 months are indispensable for the mechanical analyses inherent to this purpose, parameter data were collected. The provided dataset of morphological and segment inertial parameters is a valuable tool for locomotor biomechanical modelling. Analysis of the parameter data showed that there are substantial changes of most segment inertial parameters across body length and body mass. In addition, a classification system was developed to categorize toddlers on the basis of morphometry, reflecting the segment inertial constitution of the child. A principal components analysis (PCA) was applied to define the variance in physique between the children. PCA resulted in three newly composed variables: the ‘Axis of chubbiness’, the ‘Axis of allometric growth’ and the ‘Axis of relative limb length’. The three axes are plotted against each other, resulting in eight morphological classes. With this classification the morphotype of toddlers between 15 and 36 months can be specified and used for further research on their walking patterns.

Trunk biomechanics during hemiplegic gait after stroke: A systematic review

Stroke commonly results in trunk impairments that are associated with decreased trunk coordination and limited trunk muscle strength. These impairments often result in biomechanical changes during walking. Additionally, the so-called pelvic step might be influenced by these impairments. Therefore, the aim of this review was twofold. First, to gain more insight into trunk biomechanics during walking in stroke patients compared to healthy individuals. Second, to investigate the influence of walking speed on trunk biomechanics. The search strategy was performed by the PRISMA guidelines and registered in the PROSPERO database (no. CRD42016035797). Databases MEDLINE, Web of Science, Cochrane Library, ScienceDirect, and Rehabdata were systematically searched until December 2016. Sixteen of the 1099 studies met the eligibility criteria and were included in this review. Risk of bias was assessed by the Newcastle-Ottawa Scale. The majority of studies reported on trunk kinematics during walking, data on trunk kinetics and muscle activity is lacking. Following stroke, patients walk with increased mediolateral trunk sway and larger sagittal motion of the lower trunk. Although rotation of the upper trunk is increased, the trunk shows a more in-phase coordination. Acceleration of the trunk diminishes while instability and asymmetry increase as there are less movement towards the paretic side. However, it is of great importance to differentiate between compensatory trunk movements and intrinsic trunk control deficits. Specific exercise programs, assistive devices and orthoses might be of help in controlling these deficits. Importantly, studies suggested that more natural trunk movements were observed when walking speed was increased.

Mechanical energy estimation during walking: validity and sensitivity in typical gait and in children with cerebral palsy.

Gait efficiency in children with cerebral palsy is usually quantified by metabolic energy expenditure. Mechanical energy estimations, however, can be a valuable supplement as they can be assessed during gait analysis and plotted over the gait cycle, thus revealing information on timing and sources of increases in energy expenditure. Unfortunately, little information on validity and sensitivity exists. Three mechanical estimation approaches: (1) centre of mass (CoM) approach, (2) sum of segmental energies (SSE) approach and (3) integrated joint power approach, were validated against oxygen consumption and each other. Sensitivity was assessed in typical gait and in children with diplegia. CoM approach underestimated total energy expenditure and showed poor sensitivity. SSE approach overestimated energy expenditure and showed acceptable sensitivity. Validity and sensitivity were best in the integrated joint power approach. This method is therefore preferred for mechanical energy estimation in children with diplegia. However, mechanical energy should supplement, not replace metabolic energy, as total energy expended is not captured in any mechanical approach.

A cross-sectional study about the relationship between morphology and step-time parameters in children between 15 and 36 months

Morphology and step-time parameters were recorded in 100 children between 15 and 36 months to investigate the relation between morphology and the walking pattern. A footfall method was used to register step-time parameters. Next, the differences in step-time parameters between four morphological classes were assigned with a multiple analysis of variance. We also performed stepwise linear regressions with a correction for walking experience, to examine the relation between detailed morphological measurements and step-time parameters. The results of these regressions show a significant relation between pelvis span/ankle spread ratio and the relative radii of gyration in the frontal plane of head and pelvis. It is hypothesized that the morphology of the head and pelvis plays a role in the coordination of the walking pattern.